It is desirable to provide a driveline torque control of a machine while the engine is operating at high idle. In a wheel loader type machine, such a control allows the operator to "inch" the machine into a pile of material while providing full power to the implement hydraulics to capture the material. The driveline torque control additionally reduces rimpull, which is useful for reducing wheel slipping.
In one conventional mode of "inching" a machine, the transmission is kept in gear and the brakes are manually modulated by use of a foot pedal. This is undesirable because it requires considerable operator effort and because the service brakes experience a relatively rapid rate of wear.
In another conventional method of providing inching capabilities to a machine, an impeller clutch is connected between a machine's engine and transmission. Typically, the impeller clutch is actuated through an operator pedal. The operator pedal acts to engage and disengage the impeller clutch, thereby, varying the power transmitted by the drive train to slow the machine and reduce wheel slip. However, maintaining the machine at a speed proportional to the operator pedal is difficult due to changes in torque on the drive train.
The present invention is directed to overcoming one or more of the problems as set forth above.